With the growing demand for smaller semiconductor devices and MEMS's, in addition to conventional photolithography techniques, microfabrication technologies are gaining attention. In such a microfabrication technology, a mold having surface asperities is pressed against a resist (curable composition) on a substrate (wafer) to form a resist pattern on the substrate.
This technique is also referred to as an UV imprinting technique and can form a fine structure on the order of nanometers on a substrate. First, a resist is applied to a patterning region on a substrate in an UV imprinting apparatus. The resist is then patterned with a patterning mold. After the resist is cured by light irradiation, the mold is removed. A resin pattern (photo-cured product) corresponding to the asperities of the mold is formed on the substrate.
In the formation of the resin pattern (photo-cured product), it is desirable that the residual layer thickness of the resin pattern (photo-cured product) be made uniform on the surface of the substrate. This aims to reduce in-plane variations in line width in dry etching in a step other than a patterning step with an imprinting apparatus, for example, in an etching step, for example, in a semiconductor device manufacturing process. In order to make the residual layer thickness of a resin pattern (photo-cured product) uniform, PTL 1 discloses an imprinting method for optimizing the arrangement of resist droplets in a manner that depends on the density of a pattern to be transferred in the application of a resist on a substrate using an ink jet method. In this imprinting method for discretely arranging the resist on the substrate, however, the resist is difficult to spread on the substrate. Thus, when a patterned portion of a mold is pressed against the resist on the substrate, air bubbles often remain between the patterned portion and the resist. Curing of the resist with residual air bubbles can result in the formation of a resin pattern (photo-cured product) having an unintended shape. Waiting for the disappearance of residual air bubbles reduces productivity. PTL 2 discloses a method for promoting the disappearance of residual air bubbles by introducing a condensable gas that can condense under certain temperature and/or pressure conditions between a mold and a substrate and utilizing a volume reduction associated with the condensation of the gas. The condensable gas used in PTL 2 is trichlorofluoromethane (CFCl3). NPL 1 reports that use of 1,1,1,3,3-pentafluoropropane (CHF2CH2CF3) as a condensable gas can improve filling.
In such a condensable gas atmosphere, a large amount of gas dissolves in uncured resist. Thus, while the mold is removed from the resin (photo-cured product) on the substrate after photo-curing of the resist, the gas dissolved in the resist volatilizes and forms bubbles. NPL 2 reports that a larger amount of foaming gas causes a larger deviation from an intended shape of the photo-cured product (for example, higher surface roughness), which should be the same shape as the mold. NPL 2 recommends the use of a resist that dissolves no condensable gas. NPL 2 also describes a monomer having an ether group or a hydroxy group to reduce condensable gas solubility. However, monomers described in the literature have high viscosities and are difficult to apply using the ink jet method.
As described above, in order to prevent the formation of a cured product having an unintended shape, the amount of condensable gas that dissolves in a composition is minimized. However, the present inventors found that a larger amount of condensable gas dissolved in a composition results in a lower demolding force when the photo-cured resin is removed from the mold.
A high demolding force may result in the formation of a photo-cured product having an unintended shape because of a residual photo-cured product in a mold, fracture of a photo-cured product, or toppling of a photo-cured product pattern on a substrate, thus causing the same problem as that caused by a large amount of dissolved condensable gas. Thus, the present inventors found that, in imprinting using a condensable gas, reduction in demolding force is contradictory to reduction in surface roughness and pattern shrinkage of a photo-cured product with respect to gas solubility in a composition and that it is important to simultaneously solve these problems.